Space/time and how body's "move" in it?

Question

First a repsonse to my question about light and redshifting.

As for galaxies moving away from each other without space expanding, you just can't do that. Remember that everything is embedded IN space. An object, like a galaxy, can't move independantly of the space that contains it.

next the question that made me think of....

Why cant something move “through” the universe (space/time)? I was told nothing can move Independently throughoutt space/time, therefore space/time iteselfe must be expanding. But If that was true. Then I couldn’t throw a baseball to my dad without space/time expanding that distance every time it was tossed back and forth right?

Answer 1

First I will address your difficulty with the answer someone gave to your earlier question.

Space is expanding between distant parts of the universe, and presumably very slowly on local scales too (~100 km/s per MPC, works out to about 100 nm/s over a distance of a meter. Hmmm, I wonder if one could devise an experiment to measure that. . . )

Locally, things like gravity (in the case of a galaxy) or electromagnetic forces (in the case of a less than planet sized solid) overcome that expansion. If everything in space was expanding uniformly, we would never notice that phenomenon, because the "rulers" we use to measure distance and size would be expanding too!

So, you can throw your baseball, and maybe space will expand between the two of you as it travels, however the friction between the two of you and the ground, and the chemical bonds and electrostatic forces in the strip of ground between you and your dad do not permit the two of you to be dragged apart by the expansion of space during the ball's travel time, just as those same forces prevent your body from expanding with the expansion of space.

The answerer was incorrect in their generalization. I will take a look at this earlier question you asked; in context the part of the answer might be OK, but it appears to be too general a statement the way you presented it.

Keep questioning answers; you have the makings of a good scientist, philosopher, lawyer or other combination creative and analytical endeavour.

Your more general question was about movement in "space-time." If you define movement by a change in space-time interval, then the difficulty is in staying still! In fact, you have to move through 3-D space at the speed of light to experience zero change in the space-time interval between two events; only light itself is frozen in space-time in those terms.

Wiki has a good section on space-time intervals:
http://en.wikipedia.org/wiki/Space-time_interval#Basic_concepts

Answer 2

First consider that movement is a relative term. It relates the difference in separation of one thing to another. Objects with or without mass as well as time( the relation of the separation of 1 moment to another). Next when you think in terms of infinitency you can realize that time/space never began nor will it ever end. Also realize that the majority of space IS NOTHING. With these ideas in mind i find that "objects" can not move independently they need another "object" to be in relation to, also if space itself is nothing then a moving object can not move in relation to space.